JPH08200140A - Method for deciding combustion state of internal combustion engine and method and device for controlling combustion state of internal combustion engine - Google Patents

Abstract

PURPOSE: To perform reliable control of combustion of each cylinder by a method wherein angular acceleration of a rotary shaft driven by an internal combustion engine is detected and a combustion worsening state is decided through comparison of a detecting result with a given threshold value set according to the angular acceleration and the operation state of an internal combustion engine. CONSTITUTION: Angular acceleration of a crank shaft at an intercrank period is calculated by an angular acceleration acceleration detecting means 107 comprising a main element consisting of a crank angle sensor and a cylinder discrimination sensor. The angular acceleration is compared with a given threshold, set by a threshold updating means 110 to set and update a threshold for comparing an angular acceleration according to an engine state, by a combustion worsening decision value calculation means 104 to determine a combustion worsening decision value. The combustion worsening decision value is determined by accumulating a worsening amount with a difference between angular acceleration and a threshold serving as a weight and by reducing the influence of a numerical value approximately equal to a threshold value, a worsening state is accurately reflected. Further, a combustion state control means 105 controls a combustion fluctuation regulation element 106 in relation to a reference value from a reference value set means 112 by referring to a combustion worsening decision value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lean burn internal combustion engine (hereinafter referred to simply as "internal combustion engine") that performs lean burn operation at a leaner air-fuel ratio than the stoichiometric air-fuel ratio under required operating conditions. The present invention relates to a combustion state determination method for an internal combustion engine, a combustion state control method for the internal combustion engine, and a combustion state control device, which are suitable for use as an “engine”.

[0002]

2. Description of the Related Art In recent years, a lean burn internal combustion engine (so-called lean burn engine) has been provided which performs a lean burn operation at a leaner air-fuel ratio (lean) than a stoichiometric air-fuel ratio (stoichio) under required operating conditions. There is. In such a lean burn engine, during lean burn operation (lean burn operation), the air-fuel ratio is set as large as possible (that is, the air-fuel mixture becomes lean as much as possible) in order to reduce the NOx emission amount. The value of the fuel ratio is set near a limit (lean limit) at which the air-fuel mixture can perform stable combustion.

By performing such lean burn operation, NOx emission can be suppressed and fuel consumption can be greatly improved.

[0004]

By the way, in order to perform the lean burn operation, the control device controls the combustion state. In this control, the engine torque can be estimated from the angular acceleration of the crankshaft. It has been published in papers. However, these estimates are
It is performed for each moment using a changing instantaneous value,
It has not been considered to carry out stable and reliable control every predetermined period in consideration of the probability and statistical properties of the engine torque Pi.

Further, as shown in FIG. 12, the combustion fluctuation in the engine varies among the cylinders, and this variation is caused by the air-fuel ratio variation due to the deviation of the injector, the shape of the intake pipe, the valve timing and the like. Therefore, in the lean burn operation, the combustion state is controlled so as to correspond to the air-fuel ratio of the cylinder with the largest combustion fluctuation.

However, with such means, there is a problem that a cylinder with a relatively small combustion fluctuation cannot be operated at the limit air-fuel ratio. The present invention has been devised in view of such problems, and by a simple method, in lean burn operation, in consideration of the probability and statistical properties of combustion fluctuations, reliable combustion control, particularly reliable for each cylinder. An object of the present invention is to provide an engine combustion state determination method, an engine combustion state control method, and a combustion state control device capable of performing combustion control.

[0007]

Therefore, the method for determining the combustion state of the engine according to the present invention comprises the first step of detecting the angular acceleration of the rotating shaft driven by the internal combustion engine, the angular acceleration and the internal combustion engine. The second step of judging the combustion deterioration state by comparing with a predetermined threshold value set according to the operating state of No. 2 is configured.

The determination of the combustion deterioration state may be performed by detecting the state where the angular acceleration is lower than the predetermined threshold value. Further, the threshold value can be set according to at least one of the load and the rotational speed of the internal combustion engine. Further, the combustion state control method for an internal combustion engine of the present invention is set according to the first step of detecting the angular acceleration of the rotating shaft driven by the internal combustion engine, and the angular acceleration and the operating state of the internal combustion engine. The second step of setting a combustion deterioration determination value by comparing with a predetermined threshold value, and the internal combustion engine so that the combustion deterioration determination value is compared with a predetermined reference value and the combustion deterioration determination value approaches the reference value. And a third step of controlling the combustion fluctuation adjusting element of the above.

At this time, the combustion deterioration determination value may be obtained by accumulating the deterioration amounts of combustion in which the angular acceleration is below the predetermined threshold value, or the combustion deterioration determination value may be updated for each set number of combustions. . Furthermore, the combustion state control device for an internal combustion engine of the present invention is an internal combustion engine capable of operating at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, and detects angular acceleration of a rotary shaft driven by the internal combustion engine. A threshold value setting means for setting an angular acceleration comparison threshold value according to the operating state of the internal combustion engine, the angular acceleration detected by the angular acceleration detecting means, and the threshold value setting means depending on the operating state of the internal combustion engine. By comparing with a predetermined threshold value set by, the combustion deterioration determination value calculating means for obtaining the combustion deterioration determination value, and by comparing the combustion deterioration determination value with a predetermined reference value, the combustion deterioration determination value is A combustion state control means for controlling the combustion variation adjusting element of the internal combustion engine is provided so as to approach the reference value.

[0010]

In the above-described method for determining the combustion state of the engine of the present invention, the angular acceleration of the rotating shaft driven by the internal combustion engine is detected in the first step, and the angular acceleration and the operation of the internal combustion engine are detected in the second step. The deterioration state of combustion is determined by comparing with a predetermined threshold value set according to the state.

The determination of the deterioration state of combustion may be made by detecting the state in which the angular acceleration is lower than the predetermined threshold value. Further, the threshold value can be set according to at least one of the load and the rotational speed of the internal combustion engine. Further, in the combustion state control method for an internal combustion engine of the present invention, the angular acceleration of the rotating shaft driven by the internal combustion engine is detected in the first step, and the angular acceleration and the operating state of the internal combustion engine are detected in the second step. According to a predetermined threshold value set accordingly, a combustion deterioration determination value is set, and in a third step, the combustion deterioration determination value is compared with a predetermined reference value, and the combustion deterioration determination value becomes the above reference value. The combustion fluctuation adjusting element of the internal combustion engine is controlled so as to approach.

At this time, the combustion deterioration determination value may be obtained by accumulating the amount of deterioration of combustion in which the angular acceleration falls below the predetermined threshold value, or the combustion deterioration determination value may be updated for each set number of combustions. Further, in the combustion state control device for an internal combustion engine of the present invention, in an internal combustion engine capable of operating at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, the angular acceleration detecting means detects the angular acceleration of the rotating shaft driven by the internal combustion engine. Then, the combustion deterioration determination value calculation means compares the detected angular acceleration with a predetermined threshold value set by the threshold value setting means according to the operating state of the internal combustion engine to obtain a combustion deterioration determination value, and further the combustion state. The control means refers to the combustion deterioration determination value and compares it with a predetermined reference value, and controls the combustion fluctuation adjusting element of the internal combustion engine so that the combustion deterioration determination value approaches the reference value.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An engine combustion state determination method, an engine combustion state control method and a combustion state control apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an apparatus for carrying out the method. 2 is a block diagram of an engine system having this device, FIG. 3 is a hardware block diagram showing a control system of an engine system having this device, and FIGS. 4 and 5 are for explaining the operation of this device. 6 is a waveform diagram for explaining the operation of the apparatus, FIG. 7 is a correction characteristic diagram for explaining the operation of the apparatus, and FIG. 8 is a schematic graph for explaining the operation of the apparatus. 9, FIG. 9 is a schematic graph for explaining the operation of the present device, FIG. 10 is a characteristic diagram of a threshold correction value for explaining the operation of the present device, and FIG. 11 is a schematic diagram showing an angular acceleration detection unit in the present device. Perspective view A.

An engine for an automobile equipped with this device has a stoichiometric air-fuel ratio under required operating conditions.
It is configured as a lean burn engine that performs lean burn operation (lean burn operation) at a leaner air-fuel ratio (lean) than this, and this engine system is as shown in FIG. That is, in FIG. 2, an engine (internal combustion engine) 1 has an intake passage 3 and an exhaust passage 4 communicating with a combustion chamber 2 thereof, and the intake passage 3 and the combustion chamber 2 are controlled to communicate with each other by an intake valve 5. In addition, the exhaust passage 4 and the combustion chamber 2 are controlled to communicate with each other by an exhaust valve 6.

Further, the intake passage 3 is provided with an air cleaner 7, a throttle valve 8 and an electromagnetic fuel injection valve (injector) 9 in this order from the upstream side, and the exhaust passage 4 is provided in order from the upstream side. A three-way catalyst 10 and a muffler (silencer) not shown are provided. The injector 9 is provided for each cylinder of the engine 1. Further, the intake passage 3 is provided with a surge tank 3a.

The three-way catalyst 10 purifies CO, HC and NOx under stoichiometric operation and is a known one. Further, the throttle valve 8 is connected to an accelerator pedal (not shown) via a wire cable, and its opening degree is adjusted according to the depression amount of the accelerator pedal.

A first bypass passage 11A for bypassing the throttle valve 8 is provided in the intake passage 3, and a stepper motor valve (hereinafter referred to as an STM valve) which functions as an ISC valve is provided in the first bypass passage 11A. 12 are installed. In addition, in the first bypass passage 11A,
A wax-type fast idle air valve 13 whose opening is adjusted according to the engine cooling water temperature is also provided, and is attached to the STM valve 12.

Here, the STM valve 12 is a valve body 12a which can abut against a valve seat portion formed in the first bypass passage 11A.
And a stepper motor (I
(SC actuator) 12b, and a spring 12c that urges the valve body in a direction that presses the valve body against the valve seat portion (a direction that closes the first bypass passage 11A). The stepper motor 12b performs stepwise adjustment of the position of the valve body 12a with respect to the valve seat portion (adjustment by the number of steps) to open the valve seat portion and the valve body 12a, that is, the STM valve 12
The opening degree of is adjusted.

Therefore, the opening degree of the STM valve 12 is an electronic control unit (ECU) 2 as a controller which will be described later.
By controlling with 5, the intake air can be supplied to the engine 1 through the first bypass passage 11A regardless of the driver's operation of the accelerator pedal, and the throttle bypass intake amount is adjusted by changing the opening degree. You can do it.

As the actuator for ISC,
A DC motor may be used instead of the stepper motor 12b. Further, the intake passage 3 is provided with a second bypass passage 11B that bypasses the throttle valve 8, and an air bypass valve 14 is interposed in the second bypass passage 11B.

Here, the air bypass valve 14 has a second
It is composed of a valve body 14a capable of contacting a valve seat portion formed in the bypass passage 11B, and a diaphragm type actuator 14b for adjusting the position of the valve body, and a diaphragm chamber of the diaphragm type actuator 14b is provided with: A pilot passage 141 communicating with the intake passage on the downstream side of the throttle valve is provided.
An air bypass valve control solenoid valve 142 is provided at 41.

Therefore, by controlling the opening of the solenoid valve 142 for controlling the air bypass valve by the ECU 25, which will be described later, in this case also, regardless of the operation of the accelerator pedal by the driver, the second bypass passage 11B is used. The intake air can be supplied to the engine 1, and the throttle bypass intake air amount can be adjusted by changing the opening thereof. The air bypass valve controlling solenoid valve 142 is opened during lean burn operation,
Other than that, the basic operation is to be closed.

An exhaust gas recirculation passage (EGR passage) for returning exhaust gas to the intake system is provided between the exhaust passage 4 and the intake passage 3.
The EGR passage 80 is provided with an EG
The R valve 81 is interposed. Here, this EGR valve 81
Is composed of a valve body 81a capable of contacting a valve seat portion formed in the EGR passage 80, and a diaphragm type actuator 81b for adjusting the position of the valve body, and is provided in a diaphragm chamber of the diaphragm type actuator 81b. Is provided with a pilot passage 82 communicating with the intake passage downstream of the throttle valve.
An ERG valve control solenoid valve 83 is interposed in the.

Therefore, by controlling the opening degree of the EGR valve controlling solenoid valve 83 by the ECU 25 described later, the E
The exhaust gas can be returned to the intake system through the GR passage 80. In FIG. 2, reference numeral 15 denotes a fuel pressure regulator, which operates by receiving a negative pressure in the intake passage 3 and regulates the amount of fuel returned from a fuel pump (not shown) to the fuel tank. Thus, the pressure of fuel injected from the injector 9 is adjusted.

Various sensors are provided to control the engine system. First, as shown in FIG. 2, the intake air that has passed through the air cleaner 7 is introduced into the intake passage 3
An air flow sensor (intake air amount sensor) 17 that detects the intake air amount from the Karman vortex information and an intake air temperature sensor 1 that detects the temperature of the intake air of the engine 1
8. An atmospheric pressure sensor 19 for detecting atmospheric pressure is provided.

Further, the throttle valve 8 in the intake passage 3
In addition to the potentiometer-type throttle position sensor 20 that detects the opening of the throttle valve 8, an idle switch 21 is provided in the portion where is arranged.

Further, on the exhaust passage 4 side, a linear oxygen concentration sensor (hereinafter simply referred to as "linear O ₂ concentration" for linearly detecting the oxygen concentration (O ₂ concentration) in the exhaust gas on the lean side of the air-fuel ratio).
₂ sensor ”), and as other sensors, a water temperature sensor 23 that detects the temperature of the cooling water for the engine 1 and a crank angle sensor 24 (this crank angle sensor) that detects the crank angle shown in FIG. 24 also has a function as a rotation speed sensor for detecting the engine rotation speed Ne), a vehicle speed sensor 30, and the like.

The detection signals from these sensors and switches are input to the ECU 25 as shown in FIG. Here, the hardware configuration of the ECU 25 is as shown in FIG.
Is configured as a computer having a CPU (arithmetic unit) 26 as its main part, and the CPU 26 includes an intake air temperature sensor 18, an atmospheric pressure sensor 19, a throttle position sensor 20, a linear O ₂ sensor 22, and a water temperature sensor 23. The detection signal from the input interface 28
And is input via the analog / digital converter 29.

The CPU 26 also includes an air flow sensor 17, an idle switch 21, a crank angle sensor 24,
Detection signals from the vehicle speed sensor 30, the cylinder discrimination sensor 230, etc. are directly input through the input interface 35. Further, the CPU 26 transmits / receives data to / from a ROM (storage means) 36 which stores various data in addition to program data and fixed value data and a RAM 37 which is updated and sequentially rewritten via a bus line. Has become.

Further, as a result of the calculation by the CPU 26, EC
From U25, a signal for controlling the operating state of the engine 1, such as a fuel injection control signal, an ignition timing control signal,
Various control signals such as an ISC control signal, a bypass air control signal and an EGR control signal are output. Here, the fuel injection control (air-fuel ratio control) signal is sent to the CPU 26.
Is output to the injector solenoid 9a for driving the injector 9 (accurately, the transistor for the injector solenoid 9a) via the injection driver 39, and the ignition timing control signal is output from the CPU 2
6 is output to a power transistor 41 via an ignition driver 40, and a spark is sequentially generated from the power transistor 41 to an ignition plug 42 by a distributor 43 via an ignition coil 42.

The ISC control signal is output from the CPU 26 to the stepper motor 12b via the ISC driver 44, and the bypass air control signal is output from the CPU 26 via the bypass air driver 45 to the air bypass valve controlling solenoid valve. It is adapted to be output to the solenoid 142a of 142. Further, the EGR control signal is sent to the CPU2.
6 through the EGR driver 46 to the solenoid 83a of the ERG valve control solenoid valve 83.

Now, focusing on the fuel injection control (air-fuel ratio control), as shown in FIG. 1, the combustion deterioration determination value calculation means 104, the combustion state, for this fuel injection control (injector drive time control). The control means 105, the combustion fluctuation adjusting element 106, the angular acceleration detecting means 107, and the threshold updating means 110 are provided with the functions. The ECU 25
Has a function of a part of the angular acceleration detection means 107, the combustion deterioration determination value calculation means 104, the combustion state control means 105, and the threshold value updating means 110.

Here, the combustion fluctuation adjusting element 106 adjusts the fuel injection pulse width Tinj to a desired state by the control signal from the combustion state control means 105 to perform lean burn operation of the air-fuel ratio to be realized. , Injector 9
Function as the combustion fluctuation adjusting element 106. The fuel injection pulse width Tinj is expressed by the following equation.

Tinj (j) = TB · KAC (j) · K
KAFL + Td TB in this equation is the basic drive time of the injector 9, and one revolution of the engine from the intake air amount A information from the air flow sensor 17 and the engine speed N information from the crank angle sensor (engine speed sensor) 24. The intake air amount A / N information is calculated, and the basic drive time TB is determined based on this information.

Further, KAFL is a leaning correction coefficient, which is determined from the characteristics stored in the map in accordance with the operating state of the engine, and the air-fuel ratio can be made lean or stoichiometric in accordance with the operating state. ing. Then, KAC (j) is a correction coefficient for performing combustion state control corresponding to combustion fluctuation, as described later.

Further, the correction coefficient K is set according to the engine cooling water temperature, the intake air temperature, the atmospheric pressure, etc., and the driving time is corrected according to the battery voltage by the dead time (ineffective time) Td. There is. Further, the lean burn operation is configured to be performed when the lean operation condition determining means determines that a predetermined condition is satisfied.

As a result, the ECU 25 has a function of air-fuel ratio control means for controlling the air-fuel ratio so that the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio under the required operating conditions. By the way, the combustion state control device of the present embodiment is provided with an angular acceleration detecting means 107 for detecting the angular acceleration of the rotating shaft (crankshaft) driven by the engine, and the angular acceleration detecting means 107 is configured as follows. Has been done.

That is, as shown in FIG. 11, the angular acceleration detecting means 107 has a crank angle sensor 24, a cylinder discrimination sensor 230, and an ECU 25 as a controller as main elements.
It has a rotating member 221 that rotates integrally with the crankshaft 201 of the engine. The first, second and third vanes 221 protruding in the radial direction are provided on the periphery of the rotating member 221.
A, 221B, 221C are formed, and a detection unit 222 equipped so as to face the vanes 221A, 221B, 221C from both sides passes through the vanes 221A, 221B, 221C as the rotating member 221 rotates. Is detected optically or electromagnetically, and a corresponding pulse output is performed.

The vanes 221A, 221B, 22
Each of 1C has a circumferential length corresponding to a crankshaft rotation angle of a constant angle, and is spaced apart at a predetermined angular interval in the circumferential direction. That is, the opposite edges of the adjacent vanes are arranged at an angular interval of 120 degrees from each other.

By the way, the cylinder discrimination sensor 230 is fixed to a cam shaft (not shown), and is connected to the crank shaft 20.
While 1 rotates twice and the camshaft rotates once, a pulse output is generated every time the camshaft takes a specific rotational position corresponding to one cylinder. The device of this embodiment mounted on a 6-cylinder engine in which the ignition operation is performed in the order of the cylinder numbers is, for example, the third vane 2
The edge of 21C (front end 221C 'or rear end) is the detection unit 2
When passing 22, the first crankshaft rotation angle region corresponding to either one of the first cylinder and the fourth cylinder (preferably, mainly the expansion stroke in the one cylinder) of the first cylinder group is passed. When the crankshaft rushes in and the edge of the first vane 221A passes the detection portion 222,
The crankshaft is adapted to be disengaged from the first rotation angle range.

Similarly, when passing through the edge of the first vane 221A, it rushes into the second crankshaft rotation angle region corresponding to one of the second and fifth cylinders forming the second cylinder group, and then, When passing through the edge of the second vane 221B, the second vane 221B is detached from the same area. Further, when passing through the edge of the second vane 221B, it rushes into the third crankshaft rotation angle region corresponding to one of the third and sixth cylinders forming the third cylinder group, and then the third vane 221C. At the time of passing the edge of the, the departure from the same area is performed.

The discrimination between the first cylinder and the fourth cylinder, the discrimination between the second cylinder and the fifth cylinder, and the discrimination between the third cylinder and the sixth cylinder are performed based on the output of cylinder discrimination sensor 230. Is configured. With such a configuration,
The detection of angular acceleration is performed as follows. That is, during engine operation, the ECU 25 sequentially receives the pulse output from the crank angle sensor 24 and the detection signal of the cylinder discrimination sensor 230, and periodically repeats the calculation.

Further, the ECU 25 uses the crank angle sensor 2
It is determined whether the pulse output from No. 4 is the one that is sequentially input after the pulse output from the cylinder determination sensor 230 is input. This makes it possible to identify which cylinder the input pulse output from the crank angle sensor 24 corresponds to, and preferably,
A cylinder that is currently executing the expansion stroke (output stroke: BTDC75 °) is identified as an identification cylinder.

Then, the ECU 25 responds to the pulse input from the crank angle sensor 24 in accordance with the identified cylinder group m.
When the entry into the crankshaft rotation angle region corresponding to (m is 1, 2 or 3) is determined, a cycle measuring timer (not shown) is started. Next, the crank angle sensor 22
When the next pulse output is input from 0, the ECU 25 determines the departure from the crankshaft rotation angle region corresponding to the identified cylinder group m, stops the time counting operation of the cycle measuring timer, and reads the time counting result.

This time measurement result is the time interval TN (n) from the time of entry into the crankshaft rotation angle region corresponding to the identified cylinder group m to the time of departure from the region, that is, two time intervals corresponding to the identified cylinder group. A cycle TN (n) determined by a predetermined crank angle is shown. here,
The subscript n in the cycle TN (n) indicates that the cycle corresponds to the n-th (current) ignition operation in the identified cylinder.

Further, the cycle TN (n) is a cycle between 120-degree crank angles of the discriminating cylinder group in the 6-cylinder engine (time interval between operating states BTDC75 ° in adjacent cylinders), and more generally, N cylinders. In the engine (720 /
N) degree crank angle cycle. The pulse output indicating the departure from the crankshaft rotation angle region corresponding to the presently identified cylinder also represents the entry into the crankshaft rotation angle region corresponding to the next identified cylinder.

Therefore, the cylinder identifying step for the next identified cylinder is executed in accordance with the pulse output, and the period measuring timer is restarted to start the period measurement for the next identified cylinder. . By such an operation, the ECU 25 causes the 120 degree crank cycle TN
Although (n) is detected, a series of states from the # 1 cylinder to the # 6 cylinder is illustrated in FIG. 6, and the 120-degree crank cycle is from TN (n-5) to TN (n). It is represented by. By using these detected values, the angular acceleration ACC (n) of the crankshaft in the period is calculated by the following equation.

ACC (n) = 1 / TN (n). {KL (m) / TN (n)-
KL (m-1) / TN (n-1)} where KL (m) is a segment correction value, which is related to the identified cylinder this time, due to variations in vane angular intervals during vane manufacturing and mounting. The ECU 25 calculates the segment correction value KL (m) by the following equation in order to perform the correction for removing the cycle measurement error.

KL (m) = {KL (m-3) * (1-XMFDKFG) + KR (n) * (XM
FDKFD)} However, XMFDKFG shows the segment correction value gain. Further, m in KL (m) is set for each corresponding cylinder group, and m = 1 for cylinder groups # 1 and # 4, m = 2 for cylinder groups # 2 and # 5, cylinder group # 3 and # 6 correspond to m = 3, respectively.
KL (1) to KL (3) are repeated as shown in.

Since m-1 in KL (m-1) means the one immediately before the corresponding m, KL (m) = KL
When (1) KL (m-1) = KL (3), KL (m) = KL (2) KL (m-
1) = KL (1), KL (m) = KL (3), KL (m-1) = KL (2). Further, KL (m-3) in the above equation indicates KL (m) of the previous cycle in the same cylinder group, and # 4
KL (m-3) at the time of calculation of cylinder is in the previous # 1 cylinder
KL (1) is used, and KL (m-3) when calculating # 1 cylinder
Uses KL (1) in the previous # 4 cylinder. KL (m-3) when calculating # 5 cylinder is KL in previous # 2 cylinder
(2) is used, and KL (m-3) at the time of calculation for the # 2 cylinder is KL (2) for the previous # 5 cylinder. KL (m-3) when calculating # 6 cylinder is KL (3) in the previous # 3 cylinder
Is used, and the KL (m-3) in the calculation of the # 3 cylinder is the KL (3) of the previous # 6 cylinder.

On the other hand, KR (n) in the above equation is obtained by the following equation. KR (n) = 3 ・ TN (n) / {TN (n) + TN (n-1) + TN (n-2)} This is the measured time from the previous measured time TN (n-2) to the current measured time.
It is a measurement value corresponding to the average measurement time up to TN (n). When calculating the segment correction value KL (m), the first-order filter processing by the segment correction value gain XMFDKFG is applied to KR (n) using the above equation. Performed using.

Further, the engine combustion state control system of the present embodiment is provided with the threshold value updating means 110. The threshold value updating means 110 is adapted to operate the engine (volume efficiency Ev having engine load information, engine rotation speed). The threshold value IACTH (Ev, Ne) for angular acceleration comparison is set and updated according to the number Ne), and for this purpose, a threshold value map that stores the threshold value IACTH corresponding to the operating state of the engine as a map, A buffer memory for temporarily storing the threshold IACTH extracted from the threshold map, and a control means for detecting the engine operating state and extracting the threshold IACTH from the threshold map according to the engine operating state and temporarily storing the threshold IACTH in the buffer memory. It has

The threshold value IACTH is set in the map such that it becomes smaller as the engine speed Ne is larger and becomes larger as the volumetric efficiency Ev is larger. Further, a reference threshold value IACTH ₀ indicating combustion fluctuation is set, and this is divided by a threshold value correction coefficient (threshold value correction value) Kth (Ev, Ne) depending on the operating state of the engine, and an angular acceleration comparison threshold value IACTH ( = IACT ₀ / Kth (Ev, N
It can also be used as e)).

In this case, Kth (Ev, Ne) is set by the characteristics shown in FIG. 10, for example.
That is, in the characteristic of FIG. 10, the horizontal axis represents the volumetric efficiency Ev, and the coefficient Kth (Ev, N
e) is plotted with the vertical axis indicating the engine speed Ne.
It is configured to adopt the characteristic of the line on the upper right side as becomes larger.

The threshold value IACTH for comparing the angular acceleration is
It is of course possible to set according to at least one of the engine load information (volume efficiency Ev) and the engine speed Ne. That is, the threshold value IACTH is set according to both the engine load information (volume efficiency Ev) and the engine speed Ne, and the engine load information (volume efficiency E
v) only, the engine speed Ne may be set.
It may be set according to only.

Further, the combustion acceleration determination value is compared by comparing the angular acceleration ACC (n) obtained by the angular acceleration detecting means 107 with a predetermined threshold value IACTH (Ev, Ne) set according to the operating state of the engine. Combustion deterioration determination value calculation means 104 for obtaining VAC (j) is provided, and the combustion deterioration determination value VAC (j) has a threshold value IACT of angular acceleration ACC (n).
It is configured to accumulate and obtain the deterioration amount below H (Ev, Ne).

That is, the combustion deterioration determination value VAC (j)
Is calculated by the following equation.

VAC (j) = Σ {ACC (J) <IACTH} *
{IACTH-ACC (J)} where {ACC (J) <IACTH} in the above equation is ACC (J) <IA
It is a function that takes “1” when CTH is established and takes “0” when it is not established, and the angular acceleration ACC (n) is a predetermined threshold value IA set according to the operating state of the engine.
When it is lower than CTH, this lower amount is accumulated as a deterioration amount.

Therefore, the combustion deterioration determination value VAC (j)
Is obtained by accumulating the deterioration amount with the difference between the threshold value IACTH and the angular acceleration ACC (j) as a weight, and the influence of the numerical value near the threshold value is reduced to accurately reflect the deterioration state. Has been done. Then, the combustion deterioration determination value calculation means 104
The predetermined threshold value IACTH in the engine operating state (Ev, Ne) is set by the threshold value updating means 110 as described above.
Is configured to be updated in response to.

The subscript j indicates the cylinder number. As the combustion deterioration determination value VAC (j), a threshold IACT (E) in which the angular acceleration ACC (n) is set according to the operating state of the engine using a simpler program.
The number of times less than v, Ne) may be accumulated (that is, VAC (j) = Σ {ACC (j) <IACTH}).

The combustion deterioration determination value calculation means 10 as described above.
The calculation result from 4 is configured to be used by the combustion state control unit 105.

That is, the combustion state control means 105 refers to the combustion deterioration determination value VAC (j) calculated by the combustion deterioration determination value calculation means 104 and refers to the combustion of the engine for the predetermined reference value from the reference value setting means 112. It is configured to control the variation adjustment element 106. As the reference values for the control of the combustion fluctuation adjusting element 106 by the combustion state control means 105, the upper limit reference value (VACTH1) set by the upper limit reference value setting means 112U and the upper limit reference value setting means 112.
The lower limit reference value (VACTH2) set by L is provided.

In the control by the combustion fluctuation adjusting element 106, the combustion deterioration determination value VAC (j) is set to the upper limit reference value (VACTH
1) and the lower limit reference value (VACTH2). That is, the combustion fluctuation adjusting element 1
As described above, the control by 06 is configured to be performed by correcting the basic injection pulse width at the time of fuel injection, and the injection pulse width Tinj (j) is configured to be calculated by the following equation. There is.

Tinj (j) = TB × KAC (j) × K × KAFL + Td Then, the correction coefficient KAC (j) in the above equation is adjusted as follows. First, the combustion deterioration determination value VAC
When (j) exceeds the upper limit reference value VACTH1, it is considered that the combustion fluctuation value has deteriorated more than a predetermined value, and the correction of the enrichment for increasing the fuel injection amount is performed by the correction coefficient KAC ( This is done by calculating j).

KAC (j) = KAC (j) + KAR · {VAC (j)
−VACTH1} This is for calculating the correction value of the rich side upper right characteristic of the correction characteristics shown in FIG. 7, and KAR is a coefficient indicating the slope of the characteristic. Then, KAC (j) on the right side shows the correction coefficient calculated in the previous calculation cycle (n-1) for the number j cylinder, and is updated by the above equation.

In FIG. 7, the abscissa indicates the combustion deterioration determination value VAC.
And the vertical axis represents the correction coefficient KAC to show the correction characteristic. On the other hand, if the combustion deterioration determination value VAC (j) is lower than the lower limit reference value VACTH2, it is considered that there is a margin for further leaning, and the lean leaning correction for reducing the fuel injection amount is performed next. Correction coefficient KAC by formula
This is done by calculating (j).

KAC (j) = KAC (j)-KAL · {VAC (j)
− VACTH2} This is for calculating the correction value of the lean side lower left characteristic shown in FIG. 7, and KAL is a coefficient indicating the inclination of the characteristic. Further, the combustion deterioration determination value VAC (j) is lower than the lower limit reference value VACTH2.
As described above, when it is equal to or lower than the upper limit reference value VACTH1, the correction coefficient KAC (j) is not changed in order to maintain the fuel injection amount in the previous state as the proper operating state.

This corresponds to the flat characteristic between the lean side lower left characteristic and the rich side upper right characteristic shown in FIG.
It forms a dead zone for correction. Here, the lower limit reference value VACTH2 and the upper limit reference value VACTH1 are combustion fluctuation target values VA
Centering around C0, the lower limit reference value VACTH2 is set to a value of (VAC0-ΔVAC), and the upper limit reference value VACTH1 is set to a value of (VAC0 + ΔVAC).

The combustion fluctuation target value VAC0 is COV (Coefficie
It is a value corresponding to the target value of nt of variance (about 10%), and the rotation fluctuation is limited for a finite period (128 cycles) by not correcting the fuel in the range of ΔVAC on both sides of the combustion fluctuation target value VAC0. The limit cycle due to an error caused by the evaluation by or calculated by a value less than the threshold is prevented.

The correction coefficient KAC (j) described above is configured to be clipped by the upper and lower limit values, and for example,
It is set so that it falls within the range of 0.9 <KAC (j) <1.1, and the shock is prevented from occurring by performing the gradual correction without performing the rapid correction, and stable control is performed. It is configured to Further, the combustion deterioration determination value VAC (j) is the set number of combustions, for example, 1
It is updated every 28 (or 256) cycles. By performing control by grasping the combustion state for a relatively long period, stable and reliable control that reflects statistical characteristics is performed. It is configured to

Since the engine combustion state determination method and the combustion state control device as one embodiment of the present invention are configured as described above, during lean burn operation, the operations shown in the flowcharts of FIGS. Done.
First, in step S1, the angular acceleration detecting means 107
The angular acceleration ACC (n) is detected by.

The calculation used for detection is based on the following equation. ACC (n) = 1 / TN (n) ・ {KL (m) / TN (n) -KL (m-1) / TN (n
-1)) Note that KL (m) is a segment correction value, and is related to the identified cylinder this time, and is corrected to eliminate cycle measurement errors due to variations in vane angle intervals during vane manufacturing and mounting. Therefore, the segment correction value KL
(M) is calculated.

KL (m) = {KL (m-3) * (1-XMFDKFG) + KR (n) * (XM
FDKFD)} However, XMFDKFG shows the segment correction value gain. On the other hand, KR (n) in the above equation is calculated by the following equation. KR (n) = 3 ・ TN (n) / {TN (n) + TN (n-1) + TN (n-2)} This is the measured time from the previous measured time TN (n-2) to the current measured time.
This is a measurement value corresponding to the average measurement time up to TN (n), and when the segment correction value KL (m) is calculated, the first-order filter processing by the segment correction value gain XMFDKFG is performed using the above-mentioned formula.

Then, in step S2, the threshold value IACTH (Ev, Ne) for comparing the angular acceleration is set according to the operating state (Ev, Ne) of the engine. After that, the operation of the combustion deterioration determination value calculation means 104 in steps S7 to S10 is executed, and the angular acceleration ACC (n).
And a predetermined threshold value IACTH set according to the operating state of the engine, and the combustion deterioration determination value V is calculated by the following equation.
AC (j) is calculated.

VAC (j) = Σ {ACC (J) <IACTH} *
{IACTH-ACC (J)} First, in step S7, the angular acceleration ACC (n)
And a difference ΔIAC (n) between a predetermined threshold value IACTH set according to the operating state of the engine and
In step S8, it is determined whether the difference ΔIAC (n) is negative.

This judgment is based on the function {ACC (J) in the above equation.
Corresponds to <IACTH}, and takes "1" when ACC (J) <IACTH is established, and "0" when it is not established.
To take the action.

That is, since ΔIAC (n) is positive when ACC (J) <IACTH, the combustion deterioration determination value VA in step S10 is passed through the “NO” route.
Accumulation of C (j) is performed, and the above function is in a state of taking "1". On the other hand, since ΔIAC (n) is negative when ACC (J) <IACTH is not established, ΔIAC (n) = 0 is executed in step S9 through the “YES” route. As a result, in step S10, the combustion deterioration determination value VAC (j) is not accumulated,
The above function is in the state of taking "0".

As a result, when the angular acceleration ACC (n) is below the predetermined threshold value IACTH set according to the operating state of the engine, as shown by points A to D in FIG. It will be accumulated as a deterioration amount. Therefore, the combustion deterioration determination value VAC (j) is equal to the threshold value.
It is obtained by accumulating the deterioration amount with the difference between IACTH and the angular acceleration ACC (j) as the weight, and the influence of the numerical value near the threshold value is reduced to accurately determine the deterioration state to the combustion deterioration determination value VAC (j). Reflected.

At this time, the combustion deterioration determination value calculation means 104
The predetermined threshold value IACTH in the above is configured and updated by the threshold value updating means 110 in accordance with the operating state (Ev, Ne) of the engine as described above. It is possible to accurately know the combustion deterioration state from the data, and it is possible to realize an operating state closer to the lean limit.

The above subscript j indicates the cylinder number, and the combustion deterioration determination value VAC (j) is accumulated for each cylinder j.

Then, step S11 is executed to judge whether or not n indicating the number of times of sampling has exceeded 128. That is, it is determined whether or not the integration section shown in FIG. 7 has elapsed. If not, the “NO” route is taken, step S13 is executed, and the number of times n is set to “1”.
Step S20 is executed without increasing and correcting the fuel. As a result, the correction coefficient KA for the injection pulse width Tinj is within the integration section of 128 cycles.
The correction relating to C (j) is not performed, and the combustion deterioration determination value VAC (j) is exclusively accumulated.

Therefore, the deterioration determination value VAC (j) is
It is updated every set number of combustions, for example, 128 cycles. By controlling by grasping the combustion state for a relatively long period, stable and reliable reflection of statistical characteristics can be achieved. Control is performed. Then, when the integration section elapses, “YE
Through the “S” route, steps S12 to S18 are executed.

First, at step S12, the number of times n is reset to "1", and then at steps S14 and S15, the reference value setting means 112 refers to the combustion deterioration determination value VAC (j) and sets it. And a predetermined reference value is compared. First, the combustion deterioration determination value VA
When C (j) is compared with the upper limit reference value (VACTH1), and the combustion deterioration determination value VAC (j) exceeds the upper limit reference value VACTH1, that is, as shown in FIG. If the amount exceeds the upper limit reference value VACTH1, which is the limit, in step S15, the correction coefficient KAC according to the following equation
Calculation of (j) is performed.

KAC (j) = KAC (j) + KAR · {VAC (j) −VACTH1} This is for calculating the correction value of the rich side upper right characteristic shown in FIG. Assuming that the fuel injection amount has deteriorated, the enrichment correction for increasing the fuel injection amount is performed by calculating the correction coefficient KAC (j). Here, KAR is a coefficient indicating the slope of the characteristic, and KAC (j) on the right side is the previous calculation cycle (n
The correction coefficient calculated in -1) is shown, and is updated by the above formula.

If the combustion deterioration determination value VAC (j) is below the lower limit reference value VACTH2, step S16 is performed.
Assuming that the “YES” route is taken and there is room for further leaning, the correction of leaning to reduce the fuel injection amount is performed by the correction coefficient KAC
This is performed by calculating (j) (see step S16). KAC (j) = KAC (j) -KAL · {VAC (j) -VACTH2} This is to calculate the correction value of the lean side lower left characteristic shown in Fig. 7, and KAL is a coefficient indicating the slope of the characteristic. .

Further, the combustion deterioration determination value VAC (j) is
When the lower limit reference value VACTH2 or more and the upper limit reference value VACTH1 or less, the “NO” route is taken in both step S14 and step S15, and the fuel injection amount is maintained in the previous state as the proper operating state. Therefore, the correction coefficient
Do not change KAC (j). This corresponds to the flat characteristic between the lean-side lower left characteristic and the rich-side upper right characteristic shown in FIG. 7, and constitutes a dead zone for correction.

Here, the lower limit reference value VACTH2 and the upper limit reference value VA
CTH1 is centered around the combustion fluctuation target value VAC0, and is the lower limit reference value.
VACTH2 to the value of (VAC0-ΔVAC), and the upper reference value VACTH1 to (VAC
The value is set to 0 + ΔVAC). Combustion fluctuation target value VAC0
Is the target value of COV (Coefficient of variance) (10%
This is a value corresponding to the combustion fluctuation target value VAC0.By not correcting the fuel in the range of ΔVAC on both sides of the combustion fluctuation target value VAC0, the rotation fluctuation can be evaluated for a finite period (128 cycles), A limit cycle due to an error caused by the calculation is prevented.

Then, step S18 is executed, and the combustion deterioration determination value VAC (j) is reset to "0". Furthermore, in step S19, when the correction coefficient KAC (j) exceeds the upper and lower limit values, it is clipped to the limit value on the exceeded side. For example, when it is set to fall within the range of 0.9 <KAC (j) <1.1, when the calculated value in step S15 exceeds 1.1, it is set to 1.1, and the calculated value in step S16. Is less than 0.9, it is set to 0.9.

As a result, a shock or the like is prevented and stable control is performed by performing the correction gradually without performing the rapid correction. And step S2
At 0, the correction coefficient KAC determined as described above
The basic injection pulse width at the time of fuel injection according to (j) is corrected. That is, the injection pulse width Tinj (j) is calculated by the following equation.

Tinj (j) = TB × KAC (j) × K × KAFL + Td By the correction of the basic injection pulse width, the combustion state control means 105 controls the combustion fluctuation adjusting element 106, and the engine is operated as desired. Lean to lean limit. Note that control of the ERG amount can also be considered as a combustion adjustment element. Although the operation is performed as described above, the present embodiment has the following effects and advantages.

(1) The combustion fluctuation estimation in consideration of the stochastic characteristics of the engine torque and the air-fuel ratio control using this estimation can be accurately and reliably performed for each cylinder by a simple method. (2) Combustion state control of the engine in consideration of the statistical characteristics of combustion fluctuations can be performed in real time and on a vehicle-mounted computer by a simple method.

(3) The cylinder pipe difference at the combustion fluctuation limit due to the variation in the air-fuel ratio due to the injector, intake pipe shape, and valve timing deviation can be reliably corrected by a simple method. It becomes possible to set the combustion limit. (4) According to the above item, NOx emission can be minimized. (5) The rotation fluctuation detection and control for each cylinder can be performed by one crank angle sensor, and more reliable lean burn control can be performed at low cost.

[0093]

As described above in detail, according to the engine combustion state determining method of the present invention as defined in claim 1, the first step of detecting the angular acceleration of the rotating shaft driven by the internal combustion engine, The second step of comparing the angular acceleration with a predetermined threshold value set according to the operating state of the internal combustion engine to determine the deterioration state of combustion makes it possible to perform the engine operation with a simple method. The combustion state control corresponding to the operating state can be reliably performed for each cylinder, which has the advantage that lean limit operation can be performed in a wider operating range.

The determination of the combustion deterioration state may be performed by detecting the state in which the angular acceleration is lower than the predetermined threshold value (claim 2). By the method, the combustion state control corresponding to the engine operating state can be surely performed for each cylinder, and the lean limit operation can be performed in a wider operating range.

Further, the threshold value can be set in accordance with at least one of the load and the rotational speed of the internal combustion engine (claim 3). In this case, the combustion deterioration is accurately obtained from the rotational angular acceleration data. You can know the condition.

Further, according to the engine combustion state control method of the fourth aspect, the first step of detecting the angular acceleration of the rotating shaft driven by the internal combustion engine, the angular acceleration and the operating state of the internal combustion engine. A second step of setting a combustion deterioration determination value by comparing a predetermined threshold value set according to
A third step of comparing the combustion deterioration determination value with a predetermined reference value and controlling the combustion fluctuation adjusting element of the internal combustion engine so that the combustion deterioration determination value approaches the reference value. Also in this case, it becomes possible to reliably control the combustion state corresponding to the operating state of the engine for each cylinder by a simple method, and there is an advantage that the lean limit operation can be surely performed in a wider operating range. .

It should be noted that the combustion deterioration determination value is obtained by accumulating the combustion deterioration amount in which the angular acceleration is below the predetermined threshold value (claim 5), or the combustion deterioration determination value is updated for each set number of combustions. (Claim 6) It is also possible to perform the control of the combustion state corresponding to the statistical characteristics of the operating state of the engine for each cylinder with a simple method, and the lean limit is achieved. The operation can be reliably performed in a wider operation range, the deterioration state of combustion can be quantitatively and reliably grasped, and more reliable combustion state control can be performed.

According to the combustion state control device for an engine of claim 7, in an internal combustion engine capable of operating at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, the angular acceleration of the rotating shaft driven by the internal combustion engine is controlled. An angular acceleration detecting means for detecting, a threshold setting means for setting an angular acceleration comparison threshold according to the operating state of the internal combustion engine, an angular acceleration detected by the angular acceleration detecting means, and the internal combustion engine for the threshold setting means. By comparing a predetermined threshold value set according to the operating state of the engine, a combustion deterioration determination value calculation means for obtaining a combustion deterioration determination value, and by comparing the combustion deterioration determination value with a predetermined reference value, The combustion state control means for controlling the combustion fluctuation adjusting element of the internal combustion engine is provided so that the combustion deterioration determination value approaches the reference value. Qi It looks like to be reliably performed for each,
There is an advantage that lean limit operation can be reliably performed in a wider operation range.

[Brief description of drawings]

FIG. 1 is a control block diagram of a combustion state determination method for an internal combustion engine, a combustion state control method for an internal combustion engine, and a combustion state control apparatus according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of an engine system having a combustion state control device as an embodiment of the present invention.

FIG. 3 is a hardware block diagram showing a control system of an engine system having a combustion state control device as one embodiment of the present invention.

FIG. 4 is a flow chart for explaining the operation of the engine combustion state control device as one embodiment of the present invention.

FIG. 5 is a flowchart for explaining the operation of the engine combustion state control device as one embodiment of the present invention.

FIG. 6 is a waveform diagram for explaining the operation of the engine combustion state control device as one embodiment of the present invention.

FIG. 7 is a correction characteristic diagram for explaining the operation of the engine combustion state control device as one embodiment of the present invention.

FIG. 8 is a schematic graph for explaining the operation of the engine combustion state control device as one embodiment of the present invention.

FIG. 9 is a schematic graph for explaining the operation of the engine combustion state control device as one embodiment of the present invention.

FIG. 10 is a threshold correction value characteristic diagram for explaining the operation of the engine combustion state control apparatus as one embodiment of the present invention.

FIG. 11 is a schematic perspective view showing an angular acceleration detection unit in the engine combustion state control device as one embodiment of the present invention.

FIG. 12 is a graph showing combustion fluctuation characteristics in a lean burn engine.

[Explanation of symbols]

1 engine (internal combustion engine) 2 combustion chamber 3 intake passage 3a surge tank 4 exhaust passage 5 intake valve 6 exhaust valve 7 air cleaner 8 throttle valve 9 electromagnetic fuel injection valve (injector) 9a injector solenoid 10 three-way catalyst 11A first bypass passage 11B 2nd bypass passage 12 Stepper motor valve (STM valve) 12a Valve body 12b Stepper motor (ISC actuator) 12c Spring 13 First idle air valve 14 Air bypass valve 14a Valve body 14b Diaphragm type actuator 15 Fuel pressure regulator 16 Spark plug 17 an air flow sensor (intake air amount sensor) 18 intake air temperature sensor 19 atmospheric pressure sensor 20 throttle position sensor 21 the idle switch 22 linear O ₂ sensor 23 water temperature sensor 24 crank angle sensor (e Gin rotation speed sensor) 25 ECU as air-fuel ratio control means 26 CPU (arithmetic unit) 28 Input interface 29 Analog / digital converter 30 Vehicle speed sensor 35 Input interface 36 ROM (storage means) 37 RAM 39 Injection driver 40 Ignition driver 41 Power transistor 42 Ignition coil 43 Distributor 44 ISC driver 45 Bypass air driver 46 EGR driver 80 Exhaust gas recirculation passage (EGR passage) 81 EGR valve 81a Valve body 81b Diaphragm actuator 82 Pilot passage 83 ERG valve control solenoid valve 83a Solenoid 104 Combustion deterioration Judgment value calculating means 105 Combustion state controlling means 106 Combustion fluctuation adjusting element 107 Angular acceleration detecting means 110 Threshold updating means 112 Reference value setting means 12U upper reference value setting means 112L lower reference value setting means 141 pilot passage 142 air bypass valve control solenoid valve 142a solenoid 221 processor 221A first vane 221B second vane 221C third vane 222 detector

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hidefumi Ishimoto 5-3-8 Shiba, Minato-ku, Tokyo Within Mitsubishi Motors Corporation (72) Tatsuya Asaoka 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Automotive Industry Co., Ltd.

Claims (7)

[Claims] 1. A first step of detecting an angular acceleration of a rotating shaft driven by an internal combustion engine, and a comparison between the angular acceleration and a predetermined threshold value set according to an operating state of the internal combustion engine. The second to judge the deterioration state
It is configured with the steps of
A method for determining the combustion state of an internal combustion engine. 2. The combustion state determination method for an internal combustion engine according to claim 1, wherein the determination of the combustion deterioration state is performed by detecting a state in which the angular acceleration is lower than the predetermined threshold value. 3. The combustion state determination method for an internal combustion engine according to claim 1, wherein the threshold value is set according to at least one of a load and a rotational speed of the internal combustion engine. 4. A combustion method in which a first step of detecting an angular acceleration of a rotating shaft driven by an internal combustion engine is compared with a predetermined threshold value set according to an operating state of the internal combustion engine. A second step of setting a deterioration determination value; and a step of comparing the combustion deterioration determination value with a predetermined reference value and controlling a combustion fluctuation adjusting element of the internal combustion engine so that the combustion deterioration determination value approaches the reference value. 3. A combustion state control method for an internal combustion engine, comprising: 5. The combustion state control method for an internal combustion engine according to claim 4, wherein the combustion deterioration determination value is obtained by accumulating the deterioration amount of combustion in which the angular acceleration is lower than the predetermined threshold value. 6. The combustion state control method for an internal combustion engine according to claim 4, wherein the combustion deterioration determination value is updated every set number of combustions. 7. An internal combustion engine capable of operating at an air-fuel ratio leaner than the theoretical air-fuel ratio, an angular acceleration detecting means for detecting angular acceleration of a rotary shaft driven by the internal combustion engine, and an operating state of the internal combustion engine. A threshold setting means for setting a threshold for angular acceleration comparison according to the angular acceleration, an angular acceleration detected by the angular acceleration detecting means, and a predetermined threshold set by the threshold setting means according to the operating state of the internal combustion engine. In comparison, a combustion deterioration determination value calculating means for obtaining a combustion deterioration determination value, and comparing the combustion deterioration determination value with a predetermined reference value, the internal combustion engine so that the combustion deterioration determination value approaches the reference value. A combustion state control device for an internal combustion engine, comprising a combustion state control means for controlling a combustion fluctuation adjusting element of the engine.